Loss of mobility and the associated loss of self- sufficiency have a dramatic impact on the elderly and on society. In 1987, the National Center for Health Statistics reported that the elderly were more likely to have problems with walking than with any other personal care activity. Often, elderly individuals can reestablish partial self-sufficiency with assistive devices such as walkers. Even though walkers are common assistive devices used by the elderly, little data exist on the biomechanics of walker use. The objective of this study is to evaluate how older individuals with differing disabilities use walkers. The long-range goal of the study is to develop better walker designs and become more knowledgeable in walker use. Subjects participating in the study will include elderly individuals who can walk without the use of assistive device ("normal gait" group), elderly individuals who require the use of a wheel-walker for ambulation and elderly individuals who require the use of a standard (non-wheeled) walker for ambulation. We will 1) perform a complete 3D kinematic analysis (including upper extremities, trunk and lower extremities) of each subject during level ground ambulation, 2) obtain electromyographic data of seven key muscle groups of the lower extremities, and gather data on the forces applied to the instrumented walker by the upper extremities. Subjects will be chosen to minimize confounding effects caused by factors such as age and disabilities. Data obtained with the instrumented walker will include the magnitude and the direction of the forces and torques applied to each walker handle (in the three orthogonal directions) throughout the full gait cycle. 3D kinematic data will include maximum and minimum major joint angles and timing of walking events. Electromyographic data will be analyzed for temporal and amplitude differences among individuals. Extensive descriptive data analysis will be performed to document the kinematic, electromyographic and kinetic (forces applied on the walker) patterns of walker users. ANOVA models will be used to determine differences among groups (no walker vs standard walker vs wheel-walker and unilateral vs bilateral deficits). It is expected that there will be statistically significant differences among the groups.